Hypercalcemia (Study Outline) 1. Background Definition: Se…
Hypercalcemia (Study Outline) 1. Background Definition: Serum calcium above the lab reference range (often >10.5 mg/dL). Pathophysiology: Results from increased bone resorption, increased GI absorption, or decreased renal excretion of calcium. Divided into PTH-dependent vs. PTH-independent causes (high-yield classification). Major etiologies: PTH-dependent: Primary hyperparathyroidism (most common outpatient). Tertiary hyperparathyroidism (long-standing CKD). PTH-independent: Malignancy-associated hypercalcemia (most common inpatient). PTHrP-producing tumors, bone metastases, lymphoma (↑ calcitriol). Vitamin D excess. Granulomatous disease (sarcoidosis → ↑ 1-α–hydroxylase). Medications: thiazides, lithium. Endocrine disorders: hyperthyroidism, adrenal insufficiency. Misc: Milk-alkali syndrome, immobilization. 2. History Classic symptoms (stones, bones, groans, psychiatric overtones): Kidney stones, polyuria, polydipsia. Bone pain, fractures (in severe disease). Abdominal pain, constipation, nausea. Fatigue, depression, cognitive changes, confusion. Etiology clues: Malignancy: weight loss, night sweats. Hyperparathyroidism: history of kidney stones, bone pain, osteoporosis. Granulomatous disease: respiratory symptoms, uveitis. Medication use: thiazides, lithium, supplements. 3. Exam Findings General: dehydration signs (polyuria → volume loss). Neuro: lethargy, slow mentation, AMS in severe cases. GI: slowed bowel sounds, constipation. Renal: flank pain if nephrolithiasis; CVA tenderness if obstruction. Endocrine clues: thyroid enlargement (hyperthyroidism), lymphadenopathy (malignancy), sarcoid skin lesions. Bone tenderness in advanced disease. 4. Making the Diagnosis Initial labs: Total and ionized calcium (corrected Ca²⁺ if albumin low). PTH level → major branch point: High or inappropriately normal PTH → PTH-dependent causes. Low PTH → PTH-independent (malignancy, vitamin D excess, granulomatous disease). Additional labs based on PTH status: If PTH high: Serum phosphate low (typical of primary hyperparathyroidism). If PTH low: PTHrP (malignancy). 25-OH vitamin D (toxicity). 1,25-OH₂ vitamin D (granulomatous disease, lymphoma). Renal function to assess for CKD-related disorders. Urine calcium: helps differentiate hyperparathyroidism vs. familial hypocalciuric hypercalcemia. Imaging: Consider malignancy screening if suspicion high. Bone density in chronic hyperparathyroidism. Gold Standard: Lab-confirmed elevated calcium with evaluation of PTH to determine etiology. 5. Management (Exam Concepts) (No real-time treatment recommendations or dosing — conceptual principles only.) General principles: Identify and address underlying cause. Ensure adequate hydration conceptually (volume status is key). Avoid nephrotoxins; adjust renally cleared medications. Indications for urgent management (exam clues): Severe hypercalcemia with neurologic symptoms. Calcium levels significantly above normal with dehydration. Conceptual therapeutic approaches: Volume management: correct volume depletion first (concept-level). Bone resorption reduction: antiresorptive therapy concepts sometimes tested (no specifics). Address PTH-independent causes: Malignancy-associated hypercalcemia: treat underlying cancer conceptually. Granulomatous disease: immunologic modulation concepts. Renal replacement therapy: considered conceptually for severe, refractory cases or in advanced renal failure. Monitoring: Serial calcium levels. Renal function and urine output. ECG monitoring in severe cases (short QT interval is classic). Referral: Endocrinology for hyperparathyroidism, unexplained hypercalcemia, or suspected malignancy-associated processes. QUESTION A 60-year-old man presents to his primary care provider with fatigue, constipation, and mild confusion for the past two weeks. He also reports a 10-lb unintentional weight loss over the past month and increasing thirst. He has no significant past medical history and takes no medications or supplements. Vitals are normal. Physical exam reveals mild dehydration but no lymphadenopathy or palpable masses. Laboratory studies show: Total calcium: 13.2 mg/dL (reference: 8.5–10.5) Albumin: 4.2 g/dL Serum creatinine: 1.3 mg/dL (baseline: 1.0) Parathyroid hormone (PTH): 8 pg/mL (reference: 15–65) PTH-related peptide (PTHrP): elevated 25-hydroxy vitamin D: normal Which of the following is the most likely cause of this patient’s hypercalcemia? A) Primary hyperparathyroidismB) SarcoidosisC) Malignancy-associated hypercalcemiaD) Vitamin D toxicity